Internal combustion engine generates combustion noise generated when combustion of a fuel occurs, which can be classified into direct combustion noise that is generated by combustion exciting force in a cylinder and indirect combustion noise that is generated when the combustion exciting force is applied to moving components with a gap therebetween. In order to reduce the combustion noise, fuel injection control by pilot injection is performed in the engine, particularly a diesel engine having a high compression ratio.
In the pilot injection, a total amount of fuel injection is classified into a main injection amount and a pilot injection amount and fuel injection points are divided on the basis of a top dead center, thereby decreasing a pressure rise gradient of a combustion pressure in a combustion chamber. Thus, the pilot injection reduces the combustion noise by preventing the combustion pressure from rapidly increasing.
The pilot injection amount is set to be smaller the main injection amount in the total amount of fuel injection, thereby decreasing the pressure rise gradient of the combustion pressure.
For this reason, the pilot injection method for controlling combustion noise has a relatively low contribution in decreasing the pressure rise gradient of the combustion pressure, compared to a combustion robustness control method in which combustion control is performed stably against disturbances (environments, differences in fuel, engine aging, etc.) to directly control noise-vibration exciting force using a pressure sensor.
Therefore, there is a need for a technique in which the combustion robustness control method of directly controlling the noise-vibration exciting force can also control the combustion noise. Particularly, the combustion robustness control method may be matched in terms of using a high-priced combustion pressure sensor, considering a change in environment in which the combustion pressure sensor is required in the cylinder of the combustion chamber due to regulations.